Pumps are used for spraying various types of liquid substance (with the pump plus receptacle assembly commonly be called an atomizer or a sprayer) and typical substances include perfume and medicines. The volume emptied by spraying out the substance is ordinarily filled with air. However, certain substances must avoid coming into contact with air. In which case a gas, e.g. nitrogen, is injected under pressure into the receptacle with the receptacle being deliberately not completely filled with substance for spraying in order to leave space to receive the gas. As the substance is sprayed out, the nitrogen expands to occupy the volume emptied. It is difficult to inject the nitrogen after the receptacle has been filled with liquid and the pump has been crimped onto the receptacle.
The invention relates more particularly to injecting a gas (nitrogen) into receptacles fitted with precompression pumps of the type described in U.S. Pat. No. 4 025 046 or in corresponding French patents Nos. 2 305 241 and 2 314 772.